1. Field of the Invention
An aspect of invention relates to a blood pressure measuring instrument, and more particularly, to an automatic blood pressure measuring instrument and method designed to obtain a pulse wave signal and an electrocardiogram (ECG) signal from a pressure sensor and ECG electrodes, to analyze a correlation between both signals, to determine a maximum blood pressure and a minimum blood pressure based on the analyzed data, and to output the determined result to a display.
2. Description of the Related Art
As the number of the home health aged has been increased due to the general aging of society, a gradually increasing attention has been drawn to welfare and care for the aged. Thus, the approach of an elderly health care has begun to occur in a new scheme at various angles, and a concentrated attention has been paid to a blood pressure measurement functioning as the basis of health check-up.
Measurement of a blood pressure, as one of current generalized clinical tests, is carried out while a doctor performs an examination or a particular surgical operation. Further, values of blood pressure, which are measured in respective ventricle and atrium of the heart or in a peripheral vascular system, function as a basis of health check-up helpful to enable the doctor to understand an integrated function between vascular and cardiac systems.
A blood pressure refers to one generated when blood flowing a blood vessel acts on a wall of the blood vessel, and is determined by a quantity of the blood and a resistance of the blood vessel, such as elasticity, expansion, contraction and so on. Measurement of the blood pressure allows for estimation of a function of the heart or the blood vessel. To be more specific, while the heart is contracted, the blood is driven to circulate around the whole body. The pressure of the driven blood, or the maximum blood pressure, represents a contractile force of the heart. The minimum blood pressure when the heart is expanded can be considered as an index indicating how smoothly the blood circulates through the blood vessel.
The human blood vessel consists of an artery through which blood exits from the heart toward the whole body, a vein through which blood enters from the whole body toward the heart, and a capillary vessel interconnecting between the artery and the vein. In general, a pressure in the artery, i.e., an arterial blood pressure, is called a “blood pressure.” This blood pressure is very different according to size and position of the blood vessel, and is sequentially lowered in the order of an aorta, an artery, an arteriole, a capillary vessel, a veinlet, a vein and a hollow. For this reason, the blood pressure is named for the name of the blood vessel, for example, as an aortic blood pressure, an arterial blood pressure, an arteriole blood pressure and so forth. The arterial blood pressure maintained by heartbeats is one of fundamental, usual clinical symptoms estimating a function between the vascular and cardiac systems, and a factor taking part in perfusion of the entire tissues, or particularly having an important influence on a cerebral blood flow and a coronary blood flow.
As existing blood pressure measuring methods, there are an invasive one and non-invasive one. The invasive method inserts a catheter directly into an artery to measure the blood pressure. However, it requires much trouble and heavy cost in measuring the blood pressure, and has various disadvantages, such as circulatory problem of the blood, infection, blood clot and so on, in the course of inserting the catheter into the artery. For these reasons, the invasive method has been used in an extremely limited range. By contrast, the non-invasive method mainly makes use of a cuff. However, the non-invasive method is not only very inaccurate, but also is responsible for a tissular trauma. Further, it is impossible to apply to infants or low blood pressure patients, and above all to perform continuous monitoring. Additionally, an electronic hemadynamometer, which has been frequently used at the present time, shows a tendency of its accuracy to be significantly lowered when the blood pressure is less than 70 mmHg.
To measure the blood pressure, there have been many attempts to make use of a pulse wave velocity. Further, there has been devised a blood pressure estimating method using the pulse wave velocity or a pulse arrival time by many persons. However, in the case of using only the pulse wave velocity or the pulse arrival time, it is impossible to ensure accomplishment of reliable blood pressure monitoring